Field of the Invention
Example embodiments relate generally to nuclear reactors, and more particularly to a method and apparatus for a high-temperature deposition solution injector to deliver an ambient temperature deposition solution to a high temperature, high pressure feed-water flow line. In particular, the method and the apparatus ensures that the deposition solution is delivered in a location within the feed-water that is beyond the boundary layer of the flowing water, to prevent excessive deposition of the solution on the feed-water pipe just downstream of the injection tap and to prevent deposition of the solution within the injection tap, causing blockage of the tap.
Related Art
In a nuclear reactor, deposition solutions are often injected into a high temperature/pressure feed-water line in order to deposit materials on reactor surfaces. In particular, as shown in FIG. 1, hydrogen injection 2 may be used to inject hydrogen in a feed-water suction line 4b (the suction line 4b is the inlet to feed-water pumps 10) to act as an oxygen scavenger for the water circulating in the reactor 8. In conjunction with the hydrogen injection 2, a noble metal (e.g., platinum) deposition solution injection system 6 may be used to inject a deposition solution into the feed-water discharge line 4a in order to deposit platinum ions on surfaces of the reactor 8. While a Boiling Water Reactor (BWR) 8 configuration is depicted in FIG. 1, it should be understood that other types of nuclear reactors could also make use of deposition solution injections (such as the platinum deposition solution described herein). The platinum deposition solution may be, for example, a platinum salt solution of sodium hexahydroxyplatinate (Na2Pt(OH)6). By injecting the solution into the feed-water discharge 4a, platinum ions may deposit onto surfaces of the reactor 8 so that the platinum may act as a catalyst to react the injected hydrogen with oxygen molecules that may be present in the reactor. By causing hydrogen to react with oxygen molecules on surfaces of the reactor 8, water (H2O) molecules may be produced. This reaction acts to reduce and potentially eliminate oxygen molecules present on surfaces of the reactor 8 that may otherwise promote corrosion of metal components, thereby extending the useful life of reactor components.
As shown in FIG. 2, a conventional deposition solution injector configuration 12 may include a chemical feed skid 24 supplying a deposition solution to the feed-water discharge line 4a. The chemical feed skid typically provides the chemical deposition solution at ambient temperatures with a flow-rate of around 50-120 cm3/minute and a pressure typically less than 1250 psi (via positive displacement pumps). A chemical feed line 26 may provide the deposition solution from the chemical feed skid 24 to the injection tap 20. One or more injector valves 14 may be included in the chemical feed line 26 to provide shutoff for the deposition solution in the chemical feed line 26. Typically, a pipe stub 16 is included at the valve 14 discharge. A weldment 18 may connect the injection tap 20 to the pipe stub 16 and feed-water discharge line 4a. 
Because a distal end of a conventional injection tap 20 may extend only to an inner surface of the feed-water discharge line 4a, deposited material 22 may form within the end of the injection tap 20. The deposited material 22 may form at the injection point 6, as the ambient (i.e., low) temperature deposition solution is mixed with intruding eddy flow of the high temperature, high velocity feed-water (ranging between 260 and 420° F. with a flow velocity of about 10-20 ft/sec) that may cause the deposition solution to break down into platinum ions which are then deposited within the inner distal end of the injection tap 20 (it is noted that sodium hexahydroxyplatinate, Na2Pt(OH)6, begins to break down at temperatures of 300-500° F.). Blockage of the injection tap 20 caused by the deposited material 22 may cause the positive displacement pumps to increase injection pressure to provide the specified injection flow rate. Pressure may increase to the design pressure of the injector configuration 12, resulting in termination of an injection before all of the deposition solution is injected. This may cause a reduced amount of platinum to be deposited within the reactor 8, itself. Furthermore, blockage of the injection tap 20 may prevent performance of the next scheduled injection (typically done once per year), or require an unplanned reactor shutdown to remove the blockage.
In addition to blockage of the injection tap 20 by deposited material 22 within the injection points 6, smearing of deposited material 22 may also occur along the inner surfaces of the feed-water line 4a as the slowly flowing deposition solution is unable to escape the boundary layer and enter the bulk flow of the feed-water. The smearing may cause significant amounts of platinum ions to deposit along the inside of the feed-water line where it is not needed or desired, which also may reduce the amount of platinum that reaches the reactor 8.